Case studies of the effects of kelp harvesting in UK and European waters

Case studies on the effects of harvesting of kelp elsewhere in the world

Around the world numerous kelp species have been exploited over the years as a source of chemicals for industry. Since early times, kelp cast up on the shore has, along with other seaweeds, been collected for use as an agricultural fertiliser (rich in potash and phosphate) and also to improve the soil structure. In more recent times, kelp has been burned to produce iodine-rich ash but now is the basic resource used in the important alginate industry which produces valuable emulsifying and gelling agents. In Europe, kelp is now harvested from living kelp beds, the most commonly harvested species being Laminaria hyperborea and L. digitata. Commercial interest has also been increasing recently in utilising Alaria esculenta and L. saccharina as "sea vegetables" and it is possible that these species also will be harvested in the near future. This harvesting may alter or destroy the structure of the kelp forest ecosystem and reduce the POM and DOM available to other biotopes in coastal areas.

As a result of the importance of L. digitata and L. hyperborea to the chemical industry, several reviews of the effects of harvesting on kelp populations have been produced in recent years in France, Scotland and Norway.

The following brief discussion of the effects of harvesting on kelp biotopes has been extensively abstracted from the work of Martin Wilkinson (1995): "Information review on the impact of kelp harvesting".

Examples discussed below include non-European kelp species as these include some useful information on the effects of kelp harvesting on the non-kelp species in the kelp beds. Relatively little work on other species in kelp biotopes has been undertaken in the UK as commercial, mechanical harvesting of kelp has not occurred.

Impact information comes from two sources: the removal of kelp for scientific experiments, and from observations made on harvested grounds in Norway and Brittany. The observations and data need to be considered in two different ways, the effect of harvesting on the resource itself and the effect of kelp harvesting on the complete kelp forest ecosystem. Not surprisingly most published work concerns the resource rather than the entire ecosystem. The international scientific community recognises the difficulty of determining both the short-term impacts of kelp harvesting and the long-term consequences to the coastal environment. Around the coasts of Brittany 75-80,000 t of seaweed are collected each year and yet there is no data on the effects of this biomass loss from coastal ecosystems (Dauvin, 1997).

Experimental canopy removal and clearance experiments

Laminaria hyperborea harvesting

Harvesting of Laminaria digitata

The following information has been abstracted from Wilkinson 1995, (chapter 6, prepared by T. Telfer).

Most of the information on kelp harvesting that is available in the literature concentrates on community dynamics of the kelp and the effects on grazers of total or partial canopy removal. This may give an indication of harvesting effects but must be interpreted with great care. The major effects shown by the removal of kelp plants are centred on the influence of grazing populations, particularly the urchins which can increase in abundance and change kelp-dominated areas into coralline "barrens" (Keats, 1991).

Harvesting of Laminaria longicruris

Harvesting of Ecklonia species

Harvesting of Lessonia species.

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